Coating compositions for containers used in the food and beverage industries are generally expected to meet a number of relatively stringent requirements in order to be commercially acceptable. The coating should adhere well to the base material, such as a metal, and should possess flexibility, extensibility, and adhesion characteristics so as to withstand the processing of the container itself. The coating should also be able to resist the heat, steam and pressure conditions often encountered during processing of the container and its contents. Additionally, the coating itself should not affect the taste of a food or beverage if it is put inside the container. Finally, the coating should be able to withstand degradation during storage of the cans, particularly when the cans are subjected to high ambient temperature and humidity.
Food container coatings are subjected to steam processing and prolonged bake cycles. Steam processing often causes a defect in container coatings called “blush”, which is a haziness in the film thought to be caused by absorption of water. Blush is particularly evident with container coatings that are subjected to high temperature and high humidity conditions during steam processing. Another form of coating degradation called “tropical decay”, can also occur when cans, filled or unfilled, are stored in conditions of high ambient temperature and humidity.
Container coating compositions having improved resistance to defects caused by steam processing, such as water spotting, decreased solvent resistance, decreased abrasion resistance and decreased gloss retention, are desired, as are coatings that further offer resistance to tropical decay.